In the field of medical x-ray diagnostics the development of high-resolution radiation detectors is of decisive importance for the meaningfulness of recordings of a medical imaging device and thus ultimately also for the possibilities of diagnosis.
While the advantages of a high spatial resolution capability are obvious here, for many medical applications a good resolution of different radiation energies is also required, for example in order to be able to detect different tissue structures, of which the absorption capability can depend on the energy spectrum of the incident radiation. In order to subject the patient to the lowest possible radiation dose with the highest possible resolution, a high radiation sensitivity in the relevant spectral range is also increasingly important.
Indirect detectors in which the incident radiation is first converted into lower-energy radiation by a scintillator material and the radiation is subsequently detected by photodiodes frequently have a lower effective spatial resolution in this context.
Against this background, direct-converting detectors represent a possible alternative. In a direct-converting detector an incident radiation creates a plurality of band transitions in a fine semiconductor layer, wherein the electrons becoming free can be tapped off at individual electrodes which are attached to the side of the semiconductor facing away from the radiation.
Each electrode here corresponds to a pixel and can in such cases be in contact with read-out electronics, e.g. an ASIC, which is attached to a circuit board in parallel to the semiconductor layer. The contacting can for example be soldered here or achieved by conductive adhesive materials. To improve stability the read-out board for its part can be mounted on a base board, via which the individual signals from the read-out board are also forwarded. To this end the electronics of the read-out board can be wired to the base board.
When solder contacting is used between the electrodes on the semiconductor and the read-out board, it should be noted here that widely-used solders, because of their usually relatively high melting point, can adversely affect semiconductor materials, for example in their crystal structure, which can have a negative effect on the resolution. In U.S. Pat. No. 6,933,505 B2 a solder contacting is specified for this for which essentially tin and bismuth is to be used as solder, so that a lower melting point of 138° C. is to be achieved.
It should also be noted that the read-out board is mostly manufactured as a wafer, e.g. made of silicon, on which the corresponding electronics is structured on one side, however the base board is to be contacted on the opposing side. An obvious wiring per se here has the result that the entire read-out board on the side of the read-out electronics cannot be covered by directly converting semiconductor material but that cutouts must be provided there for the wires. At these points the detector loses its resolution, which makes the construction of large, contiguous flat-panel detectors with much greater resolution significantly more difficult, since the size of individual semiconductor detection elements must be increased for this purpose.
DE 10 2008 050 838 A1 discloses a detector module with a radiation detector element, evaluation electronics and a common carrier substrate, which are soldered in layers in each case by way of a low-temperature solder. However this arrangement is also not capable of solving the aforementioned problem.